add Events SDK

[martinkuba]

Which problem is this PR solving?

This adds an experimental implementation of the Events SDK.

As a related update, I have also updated the Events API with the following:

• replaced traceId and spanId fields in the Event interface with context field (see spec)
• added severityNumber field

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[JamieDanielson]

Thanks for working on this! I added a few non-blocking suggestions to make it easier for someone to try it out. I also added a note about setting a default severityNumber of 9 based on the spec.

[pichlermarc]

A few comments, looks good overall 👍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.82%. Comparing base (ecc88a3) to head (1e6d89f).
Report is 12 commits behind head on main.

❗ Current head 1e6d89f differs from pull request most recent head 87ad9bc

Please upload reports for the commit 87ad9bc to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4629      +/-   ##
==========================================
+ Coverage   91.04%   93.82%   +2.78%     
==========================================
  Files          89      240     +151     
  Lines        1954     5606    +3652     
  Branches      416     1125     +709     
==========================================
+ Hits         1779     5260    +3481     
- Misses        175      346     +171     

see 153 files with indirect coverage changes